Influenza viruses (Orthomyxoviruses) encompass a major group of human and animal pathogens and belong to enveloped, segmented, negative stranded RNA viruses. The segment #7 RNA of influenza A viruses encodes two important structural proteins- M1 from unspliced mRNA and M2 from a spliced mRNA. M1 is a relatively small, highly conserved protein (252 aa in type A and 248 aa in type B viruses). M1 is the most abundant protein in virus particles and plays critical roles in many aspects of virus replication. These include (i) dissociation of M1 from the M1/vRNP complex during the entry and uncoating of virus, (ii) nuclear entry of M1, (iii) interaction of M1 with vRNP to form M1/vRNP complex, (iv) role of M1 in the exit of vRNP from nucleus into cytoplasm, (v) interaction of M1 with viral glycoproteins (HA, NA and M2), (vi) membrane binding of M1, (vii) dimer/oligomer formation of M1, (viii) role of M1 in virus budding including (a) recruitment of viral components at the assembly site, (b) recruitment of host components for budding and release of virus particles, (c) virus morphology. Although there are conflicting hypotheses and results on the specific mechanism by which M1 accomplishes many of these functions, M1 must possess specific motifs or domains for carrying out these functions. Our specific objectives in this project are to investigate the role of the following motifs of M1 in virus biology: i. Nuclear localization motif, ii. Membrane binding motifs, iii. RNA/RNP binding motif, iv. Zinc finger motif, v. Glycoprotein (HA, NA, M2) binding motifs, vi. Dimer/oligomerization motif, vii. Others similar to late (L) domain including host protein recruitment motifs. Our preliminary data suggest the presence of an L domain-like motif in influenza virus M1. viii. In addition, we also plan to investigate if M1/vRNP complex or vRNP alone plays any role in selecting the budding site at the apical membrane since we and others have shown that HA, the major glycoprotein, is not the major determinant in apical budding of influenza virus. We plan to use the powerful tools of molecular biology and reverse genetics in identifying these motifs and defining their functions in the virus life cycle. Identification of these motifs and elucidation of their functions in virus biology will be important towards developing small interfering molecules for use in therapy and generating stable attenuated virus mutants for the development of live virus vaccine.